This invention relates to a process for preparing N-protected 2-aminoethanethiol (4). The process may be summarized by the following scheme: ##STR2## wherein R.sup.1 is triorganosilyl and R.sup.2 is a readily removable N-protecting group. Particularly preferred triorganosilyl protecting groups R.sup.1 and N-protecting groups R.sup.2 are described below, as are preferred conditions of reaction.
The N-protecting 2-aminoethanethiols (4) so prepared are useful in the synthesis of thienamycin. The utility of 4 in this manner is known. See, for example, European patent application No. 79101307.1 (published Feb. 20, 1980); publication number 007973/Al. This publication is incorporated herein by reference for the purpose of defining the utility of 4, which utility may be summarized by the following steps: ##STR3##
The unexpected advantage of the instant process is that it provides 4 in substantially pure form. Conventional procedures, when applied to the synthesis of 4, yield an annoying mixture of products, from which 4 is separated only with difficulty and expense. The principal courses of such conventional schemes are demonstrated by the following set of reactions: ##STR4## wherein the acylating agent RCOX (X is chloro), which establishes the N-acyl protecting group RCO, is embraced by the previously defined N-protecting group R.sup.2. ##STR5## The intermediate S-acylated species 5 is known to transfer the acyl group from sulfur to nitrogen to form 4. However, this S-acylated intermediate does participiate in the undesired reactions leading to formation of the cyclized 6, bis-acylated 7 and oxidation side 8 products.